1. Field of the Invention
The present invention relates to a medium press device for holding a medium conveyed in an ink jet printer and to an ink jet printer provided with the medium press device.
2. Background Information
It is known that in ink jet printers, a distance between an ink jet head ejecting ink and a medium largely influences on a print quality. The ink jet head is arranged to a printer chassis with good precision. Contrary to this, it is not a rare case that the medium to be carried may not keep a desired distance between the ink jet head due to occurrence of curling, existence of remaining cutting trash, attachment of foreign matter, and other factors. When conducting printing under such a state, it becomes difficult to control positions of ink droplets to be adhered onto the medium and the diameters of the droplets. As a result, there is a fear in that the print quality becomes unstable.
Contrary to this, in the conventional ink jet printer, there is proposed a mechanism for pressing a medium to be carried. For example, Patent Document 1 discloses a paper pressing mechanism including a pair of paper pressers for pressing lateral end portions of the paper to the platen. In the paper pressing mechanism, the paper pressers may be fixed to positions in accordance with a width of the paper by using setting screws. With this, the paper is pressed during printing to secure the distance between the ink jet head.
On the other hand, Patent Document 2 discloses a paper pressing mechanism including a pair of press clamps slidably provided on the platen. In the paper pressing mechanism, by depressing a press knob, a plate spring floats to thereby facilitate the insertion of end portions in a width direction of the printing paper, and by releasing the pressing force of the pressing knob, it is possible to press the end portions in the width direction of the paper.    [Patent Document 1] Japanese. Patent Application Laid-open No. Hei 4-69264    [Patent Document 2] Japanese Patent Application Laid-open No. 2004-90538
However, in the paper presser of Patent Document 1, the pressing mechanism is fixed during the paper conveyance, and hence in the case of abnormal conveyances such as the paper is slantly conveyed with respect to an intrinsic conveying direction, a zigzag conveyance case, or the other cases, the end portions of the paper may dislodge from the pressing mechanism, the end portions may bump to curl up, or may interfere with the ink jet head. In those cases, the distance with the ink jet head may not be kept, or there is a fear of becoming difficult to continue the conveyance.
On the other hand, in the press cramp of Patent Document 2, there is employed the structure in which after the insertion of printing paper, the pressing pressure of the pressing knob is released to press the end portions in the width direction of the paper against the platen side. As a result, similar to the paper presser of Patent Document 1, in the case where the paper is conveyed slantly, or the zigzag movement, the end portions of the paper may dislodge from the pressing mechanism, the end portions may bump to curl up, or may interfere with the ink jet head. In addition, in the press cramps of Patent Document 2, in the case where, along with the slant movement of the paper, etc., the press cramps are moved outside the paper in the width direction, the press cramps do not return to their original positions, and hence it becomes difficult to press the end portions of the paper to be conveyed later.
Contrary to this, a holding force by the pressing mechanism is enhanced, thereby being capable of forcedly pressing the paper at the time of the abnormal conveyance. However, in this case, frictional resistance is applied to the paper under conveyance, there is a risk of breaking the paper. This becomes markedly if the paper is conveyed slantly or in zigzag.
Contrary to this, a holding force by the pressing mechanism is enhanced, thereby being capable of forcedly pressing the paper at the time of the abnormal conveyance. However, in this case, a frictional resistance is applied to the paper under conveyance, and thus there is a risk of breaking the paper. This risk increases if the paper is conveyed slantly or in a zigzag manner.
On the other hand, in the case where the gap between the pressing mechanism and the paper is increased and the holding force by the pressing mechanism is weakened, the paper may be conveyed smoothly even if the paper is conveyed slantly or in a zigzag manner. However, as the holding force is weak, the gap between the ink jet head and the paper is not constant, resulting in degradation of the printing quality due to possible displacements of adhering positions of the ink ejected from the ink jet head.